Question about texture painting
After looking at your mesh for a few minutes, I noticed the shading was a bit off.  I recalculated the normals, and texture painting worked just fine.

Here is how it is done:

Go into edit mode and select everything.  Then in the Tool Shelf go to the shading tab.

Then click the Recalculate Normals button.



After doing this Texture Paint mode should work as expected!

One other thing that might help while Texture Painting is to re-unwrap your model.  I noticed that the UV unwrapping was very messy and jumbled.  If you don't know how, look into how to mark seams for your mesh so you can unwrap the whole mesh on one UV map with minimal stretching.  That will allow for less visible seams and a smoother workflow while painting.

I hope this helps!